Add more scalar values to tests

[AlekSi]

Description

Refs #914.

Readiness checklist

• I added tests for new functionality or bugfixes.
• I ran task all, and it passed.
• I added/updated comments for both exported and unexported top-level declarations (functions, types, etc).
• I checked comments rendering with task godocs.
• (for maintainers only) I set Reviewers (@FerretDB/core),
  Assignee, Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #984 (c630579) into main (df30711) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #984      +/-   ##
==========================================
+ Coverage   63.64%   63.69%   +0.05%     
==========================================
  Files         234      234              
  Lines       11028    11038      +10     
==========================================
+ Hits         7019     7031      +12     
+ Misses       3182     3180       -2     
  Partials      827      827              

Impacted Files	Coverage Δ
integration/shareddata/shareddata.go	81.35% <100.00%> (+3.80%)	⬆️
internal/util/version/version.go	55.00% <0.00%> (-5.00%)	⬇️
internal/handlers/common/filter.go	85.38% <0.00%> (ø)
internal/tjson/schema.go	65.04% <0.00%> (+1.62%)	⬆️
internal/handlers/pg/msg_dbstats.go	72.09% <0.00%> (+6.97%)	⬆️

Flag	Coverage Δ
integration	59.16% <100.00%> (+0.63%)	⬆️
mongodb	18.20% <100.00%> (+0.05%)	⬆️
pg	61.98% <100.00%> (+0.04%)	⬆️
tigris	25.79% <100.00%> (+1.33%)	⬆️
unit	24.93% <ø> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[noisersup]

LGTM

[rumyantseva]

LGTM